Front projection type display devices and rear projection type display devices using a spatial light modulation element such as a transmissive/reflective liquid crystal element or a micromirror array are known as large-screen display devices. The front projection type display devices and the rear projection type display devices are divided into a type in which three spatial light modulation elements are provided in correspondence with three primary colors of red, green and blue to form a color image and a type in which lights of three primary colors are projected to one spatial light modulation element in a time sharing manner to combine a color image. An ultra high pressure mercury lamp has been conventionally used as a light source of a projection type display device. However, with the recent years' commercialization of high-output blue semiconductor lasers, a projection type display device using laser light sources of three primary colors including a red semiconductor laser and a green laser by second harmonic generation (hereinafter, abbreviated as “SHG”) is being developed.
By using laser lights as monochromatic lights as light sources, it becomes possible to realize a projection type display device with a wider reproducible color range and small power consumption. A high-output light source is necessary to obtain a bright screen in the projection type display device. However, there is a limit in the output obtained by one semiconductor laser. Thus, a method for obtaining a high-output light by combining laser lights emitted from a plurality of semiconductor lasers is necessary. A known conventional projection type display device is such that a high output is obtained by multiplexing lights from solid-state light emitting elements using a focusing lens (see, for example, patent literature 1).
FIG. 12 is a diagram showing the construction of a conventional projection type display device disclosed in patent literature 1. In FIG. 12, lights emitted from solid-state light sources 101 are collimated by a lens array 102 and focused to a rod integrator 104 by a focusing lens 103. These lights are repeatedly reflected in the rod integrator 104, so that a uniform light quantity distribution can be obtained on an emergent end surface of the rod integrator 104. The emergent lights from the rod integrator 104 are irradiated to a liquid crystal spatial light modulation element 107 via a relay lens 105 and a field lens 106 to obtain uniform illumination lights.
An image on the liquid crystal spatial light modulation element 107 is projected onto an unillustrated screen by a projection lens 108. The rod integrator 104 is a rectangular parallelepipedic optical element made of glass, and the shapes of the incident and emergent surfaces thereof are similar to that of a part of the liquid crystal spatial light modulation element to be illuminated. In recent years, display screens have been more and more widened and many screens have an aspect ratio of 16:9. Accordingly, spatial light modulation elements and rod integrators also have the aspect ratio of 16:9.
Light emitting diodes, ultra high pressure mercury lamps and the like are used as solid-state light emitting elements in conventional projection type display devices. Divergent angles and light emission regions of the light emitting diodes and ultra high pressure mercury lamps are symmetric with respect to the optical axis of the rod integrator. Thus, in the conventional projection type display device, it is not necessary to particularly consider the arrangement of the light sources and the rod integrator and they can be treated as simple point light sources.
Accordingly, it is disclosed in patent literature 1 that a polarization converter is unnecessary in the construction of the conventional projection type display device in the case of using semiconductor lasers for emitting linearly polarized lights as solid-state light emitting elements, but other characteristics of the semiconductor lasers are not mentioned at all. FIG. 13 is a perspective view showing the construction of a semiconductor laser.
In FIG. 13, a semiconductor laser chip 109 includes an active layer 110 and a clad layer 111. If a current is applied to the semiconductor laser chip 109 via an unillustrated electrode, a laser light is emitted from a light emission region 112 of the active layer 110 restricted by the clad layer 111. Since the thickness of the active layer 110 is about 1 micron, energy density in the light emission region 112 increases to reach an end surface destruction if the laser light becomes a high output. Accordingly, in a high-output semiconductor laser, a length of the light emission region 112 in an X-axis direction (hereinafter, “stripe width”) is as large as 10 to 200 microns in order to avoid the end surface destruction.
A divergent angle of the laser light emitted from the semiconductor laser is 20 to 40° in Y-direction and 10 to 15° in X-direction in FIG. 13 at full width half maximum. Accordingly, if the laser light emitted from the light emission region 112 is focused by a focusing lens, focused spots having largely different aspect ratios can be formed. In this way, the emitted light from the semiconductor laser differs from the one from the light emitting diode, has a large divergent angle and a large anisotropy of the light emitting region, and cannot be handled as a simple point light source. Nevertheless, the arrangement of the rod integrator and the semiconductor lasers are not described in detail in the above patent literature 1.
An optimal value of an angle between the optical axis of the rod integrator and the outermost rays of the incident beam is determined by a relationship with an F-number of the projection lens. Since the collimated lights from the solid-state light emitting elements are focused to the rod integrator by the focusing lens in patent literature 1, a ratio of the aperture diameter of the focusing lens to a focal length directly becomes an angle of the light incident on the rod integrator. If an attempt is made to increase the number of the solid-state light emitting elements while keeping this angle, the aperture diameter of the focusing lens increases and the focal length invariably increases, which has presented a problem of enlarging the device.
[Patent Literature 1]
Japanese Unexamined Patent Publication No. 2005-300712
In order to solve the above problem, an object of the present invention is to provide a projection type display device and a light source device capable of being miniaturized and obtaining high-output lights by optimizing the arrangement of a laser light source and a homegenizer.
One aspect of the present invention is directed to a projection type display device, comprising a laser light source unit having a light emission region for emitting an elliptical laser light; a focusing lens unit for focusing the laser light emitted from the laser light source unit; a homogenizer having a rectangular incident surface on luminous flux focused by the focusing lens unit; a spatial light modulation element for modulating the laser light emitted from the homogenizer; and a projection lens for projecting the laser light modulated by the spatial light modulation element, wherein the incident surface of the homogenizer has a rectangular shape and the laser light source unit is arranged such that a longer axis direction of the light emission region and a longer side direction of the incident surface of the homogenizer are parallel.
With this construction, the laser light source unit has the light emission region for emitting an elliptical laser light, and the laser light emitted from the laser light source unit is focused by the focusing lens unit. The homogenizer is so arranged as to locate the rectangular incident surface on the luminous flux focused by the focusing lens unit, the laser light emitted from the homogenizer is modulated by the spatial light modulation element and the laser light modulated by the spatial light modulation element is projected by the projection lens. The incident surface of the homogenizer has a rectangular shape and the laser light source unit is arranged such that the longer axis direction of the light emission region and the longer side direction of the incident surface of the homogenizer are parallel.
Since the laser light source unit is arranged such that the longer axis direction of the light emission region and the longer side direction of the incident surface of the homogenizer are parallel, the laser light emitted from the laser light source unit can be efficiently introduced to the homogenizer and the arrangement of the laser light source unit and the homogenizer is optimized, wherefore miniaturization can be realized and high-output lights can be obtained from the homogenizer.
Another aspect of the present invention is directed to a light source device, comprising a laser light source unit having a light emission region for emitting an elliptical laser light; a focusing lens unit for focusing the laser light emitted from the laser light source unit; and a homogenizer having a rectangular incident surface on luminous flux focused by the focusing lens unit, wherein the incident surface of the homogenizer has a rectangular shape and the laser light source unit is arranged such that a longer axis direction of the light emission region and a longer side direction of the incident surface of the homogenizer are parallel.
With this construction, the laser light source unit has the light emission region for emitting an elliptical laser light, the laser light emitted from the laser light source unit is focused by the focusing lens unit, and the homogenizer is arranged to locate the rectangular incident surface on the luminous flux focused by the focusing lens unit. The incident surface of the homogenizer has a rectangular shape and the laser light source unit is arranged such that the longer axis direction of the light emission region and the longer side direction of the incident surface of the homogenizer are parallel.
Since the laser light source unit is arranged such that the longer axis direction of the light emission region and the longer side direction of the incident surface of the homogenizer are parallel, the laser light emitted from the laser light source unit can be efficiently introduced to the homogenizer and the arrangement of the laser light source unit and the homogenizer is optimized, wherefore miniaturization can be realized and high-output lights can be obtained from the homogenizer.
Still another aspect of the present invention is directed to a projection type display device, comprising a plurality of laser light sources; a plurality of focusing lenses provided in a one-to-one correspondence with the plurality of laser light sources for focusing the laser lights emitted from the plurality of laser light sources; a homogenizer having a rectangular incident surface on luminous fluxes focused by the plurality of focusing lenses; a spatial light modulation element for modulating the laser lights emitted from the homogenizer; and a projection lens for projecting the laser lights modulated by the spatial light modulation element, wherein the plurality of laser light sources include a red laser light source for emitting a red laser light, a blue laser light source for emitting a blue laser light and a green laser light source for emitting a green laser light; the red and blue laser light sources are arranged symmetrically with respect to the optical axis of the homogenizer; the green laser light source is arranged on the optical axis of the homogenizer; the plurality of focusing lenses include a focusing lens for red for focusing a red laser light emitted from the red laser light source on the incident surface of the homogenizer, a focusing lens for blue for focusing a blue laser light emitted from the blue laser light source on the incident surface of the homogenizer and a focusing lens for green for focusing a green laser light emitted from the green laser light before being incident on the homogenizer; and an angle between the optical axis of the homogenizer and the outermost edge of the green laser light at a focal point of the focusing lens for green is equal to an angle between the optical axis of the homogenizer and the red or blue laser light at a focal point of the focusing lens for red or the focusing lens for blue.
With this construction, the laser lights emitted from the plurality of laser light sources are focused by the plurality of focusing lenses provided in a one-to-one correspondence with the plurality of laser light sources. The homogenizer has the rectangular incident surface on the luminous fluxes focused by the plurality of focusing lenses, the laser lights emitted from the homogenizer are modulated by the spatial light modulation element and the laser lights modulated by the spatial light modulation element are projected by the projection lens. The red laser light source for emitting a red laser light and the blue laser light source for emitting a blue laser light are arranged symmetrically with respect to the optical axis of the homogenizer, and the green laser light source for emitting a green laser light is arranged on the optical axis of the homogenizer. The red laser light emitted from the red laser light source is focused on one point by the focusing lens for red, the blue laser light emitted from the blue laser light source is focused on one point by the focusing lens for blue, and the green laser light emitted from the green laser light source is focused by the focusing lens for green before being incident on the homogenizer. The angle between the optical axis of the homogenizer and the outermost edge of the green laser light at the focal point of the focusing lens for green is equal to the angle between the optical axis of the homogenizer and the red or blue laser light at the focal point of the focusing lens for red or blue.
Accordingly, the green laser light source having a more complicated construction than the red and blue laser light sources as semiconductor lasers is arranged on the optical axis of the homogenizer. Thus, the miniaturization of the device can be realized. Even if the green laser light source is arranged on the optical axis of the homogenizer, the green laser light is incident at a specified angle to the incident surface of the homogenizer. Thus, the light quantity distribution of the green laser light can be homogenized approximately to the same extent as those of the red and blue laser lights, wherefore the occurrence of color nonuniformity can be suppressed.